The Steelers controlled the second half, finally taking the lead when Ryan Shazier intercepted Brock Osweiler to set up a 23-yard dart from Roethlisberger to Brown with 3:34 to go. Pittsburgh's defense made it stand up, twice stopping the Broncos over the final minutes.
Brown, Markus Wheaton and Martavis Bryant found plenty of room to maneuver against Denver's secondary, dubbed the No Fly Zone by stars Aqib Talib and Chris Harris.
Osweiler threw for 296 yards with three touchdowns passing and another on the ground but struggled in the second half as the Broncos (10-4) lost their second straight and failed to lock up the AFC West title.
Emmanuel Sanders caught 10 passes for 181 yards and a score in his first game against his former team. Demaryius Thomas hauled in a pair of touchdowns but Osweiler completed just 7 of 26 passes over the final two quarters.
Osweiler's grasp on the starting job appeared tenuous coming in after the offense failed to find the end zone in a home loss to Oakland last Sunday. Peyton Manning returned to practice last week for the first time in a month as he continues to recover from torn plantar fascia in his left foot. The NFL's all-time passing leader traveled with the team and signed dozens of autographs in the pregame, save for any of Pittsburgh's yellow Terrible Towels, which Manning shunned when thrust his way.
Perhaps it provided inspiration for Osweiler, who spent a half forcing the Steelers to keep their favorite linens tucked safely in their pockets as Denver raced up and down Heinz Field with ease.
The Broncos had gone 24 straight possessions without an offensive touchdown before reaching the end zone four straight times. Osweiler hit Thomas for an 18-yard score then found Sanders for an easy 61-yard catch and run. Osweiler stumbled his 6-foot-7 frame across the goal line to make it 20-7 and when Thomas stiff-armed Pittsburgh's Antwon Blake to finish off a 6-yard touchdown, the Broncos were up 27-10.
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Steelers rally past Osweiler, Broncos 34-27
Sergio Brown #38 of the Jacksonville Jaguars takes the field prior to a preseason game against the Pittsburgh Steelers at EverBank Field on August 14, 2015 in Jacksonville, Florida. (Photo by Stacy Revere/Getty Images)
Odell Beckham #13 of the New York Giants catches a touchdown in front of Jairus Byrd #31 of the New Orleans Saints during the third quarter of a game at the Mercedes-Benz Superdome on November 1, 2015 in New Orleans, Louisiana. (Photo by Sean Gardner/Getty Images)
PHILADELPHIA, PA - SEPTEMBER 20: DeMarco Murray #29 of the Philadelphia Eagles leaps over Brandon Carr #39 of the Dallas Cowboys in the third quarter on September 20, 2014 at Lincoln Financial Field in Philadelphia, Pennsylvania.The Dallas Cowboys defeated the Philadelphia Eagles 20-10. (Photo by Elsa/Getty Images)
ORCHARD PARK, NY - SEPTEMBER 20: Julian Edelman #11 of the New England Patriots scores a touchdown during NFL game action as Aaron Williams #23 of the Buffalo Bills tries to make the tackle at Ralph Wilson Stadium on September 20, 2015 in Orchard Park, New York. (Photo by Tom Szczerbowski/Getty Images)
GLENDALE, AZ - FEBRUARY 01: Jermaine Kearse #15 of the Seattle Seahawks makes a catch against Malcolm Butler #21 of the New England Patriots in the fourth quarter during Super Bowl XLIX at University of Phoenix Stadium on February 1, 2015 in Glendale, Arizona. (Photo by Mike Ehrmann/Getty Images)
OAKLAND, CA - AUGUST 30: Taiwan Jones #22 of the Oakland Raiders tries to catch the ball in the endzone while covered by Chris Clemons #29 of the Arizona Cardinals at O.co Coliseum on August 30, 2015 in Oakland, California. The play was called back for a penalty and did not count. (Photo by Ezra Shaw/Getty Images)
ST. LOUIS, MO - SEPTEMBER 27: Antonio Brown #84 of the Pittsburgh Steelers is tackled by Janoris Jenkins #21 of the St. Louis Rams after making a catch in the first quarter at the Edward Jones Dome on September 27, 2015 in St. Louis, Missouri. (Photo by Dilip Vishwanat/Getty Images)
PITTSBURGH, PA - DECEMBER 6: Jesse James #81 of the Pittsburgh Steelers is tackled by Darius Butler #20 (not pictured) of the Indianapolis Colts as Mike Adams #29 of the Indianapolis Colts defends in the first quarter of the game at Heinz Field on December 6, 2015 in Pittsburgh, Pennsylvania. (Photo by Justin Aller/Getty Images)
GREEN BAY, WI - OCTOBER 11: Ty Montgomery #88 of the Green Bay Packers does the 'Lambeau Leap' after running in a 31 yard touchdown against the St. Louis Rams in the first quarter at Lambeau Field on October 11, 2015 in Green Bay, Wisconsin. (Photo by Jonathan Daniel/Getty Images)
SEATTLE, WA - JANUARY 18: The Green Bay Packers huddle in the fourth quarter of the 2015 NFC Championship game against the Seattle Seahawks at CenturyLink Field on January 18, 2015 in Seattle, Washington. (Photo by Ronald Martinez/Getty Images)
LANDOVER, MD - NOVEMBER 15: The Washington Redskins are introduced before playing the New Orleans Saints at FedExField on November 15, 2015 in Landover, Maryland. The Washington Redskins won, 47-14. (Photo by Patrick Smith/Getty Images)
TAMPA, FL - NOVEMBER 08: Jameis Winston #3 of the Tampa Bay Buccaneers drops back during a game against the New York Giants at Raymond James Stadium on November 8, 2015 in Tampa, Florida. (Photo by Mike Ehrmann/Getty Images)
DETROIT MI - DECEMBER 3: Richard Rodgers #82 of the Green Bay Packers catches a fourth quarter touchdown to win the game 27-23 over the Detroit Lions on December 3 2015 at Ford Field in Detroit, Michigan. (Photo by Leon Halip/Getty Images)
NEW ORLEANS, LA - OCTOBER 15: Benjamin Watson #82 of the New Orleans Saints scores a touchdown during the third quarter of a game against the Atlanta Falcons at the Mercedes-Benz Superdome on October 15, 2015 in New Orleans, Louisiana. (Photo by Chris Graythen/Getty Images)
EAST RUTHERFORD, NJ - NOVEMBER 08: Brandon Marshall #15 of the New York Jets attempts to catch a pass under pressure from Telvin Smith #50 and Johnathan Cyprien #37 of the Jacksonville Jaguars during the second quarter at MetLife Stadium on November 8, 2015 in East Rutherford, New Jersey. (Photo by Al Bello/Getty Images)
CLEVELAND, OH - OCTOBER 18: Strong safety David Bruton #30 of the Denver Broncos and tight end Gary Barnidge #82 of the Cleveland Browns fight for a last second throw into the end zone to end the first half at FirstEnergy Stadium on October 18, 2015 in Cleveland, Ohio. (Photo by Jason Miller/Getty Images)
ARLINGTON, TX - OCTOBER 11: Wide receiver Julian Edelman #11 of the New England Patriots dives into the endzone to score on a 59 yard touchdown reception against the Dallas Cowboys during the second half of the NFL game at AT&T Stadium on October 11, 2015 in Arlington, Texas. (Photo by Christian Petersen/Getty Images)
GLENDALE, AZ - FEBRUARY 01: Tom Brady #12 of the New England Patriots is surrounded by the media after defeating the Seattle Seahawks 28-24 during Super Bowl XLIX at University of Phoenix Stadium on February 1, 2015 in Glendale, Arizona. (Photo by Tom Pennington/Getty Images)
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Yet just as quickly a Denver's momentum appeared, it vanished. The group that converted its first eight third-downs then missed its next five, giving Roethlisberger more than enough time to have his way with the NFL's best secondary.
A pretty lob to the back corner of the end zone from Roethlisberger to Brown pulled Pittsburgh with 27-20. The Steelers then caught the break they needed thanks to some overanxious Broncos. Pittsburgh punted late in the third quarter and two Steelers attempted to down it only to whiff. A couple of Denver linemen — all the way on the other side of the field — thought the play was dead. It wasn't. Jordan Norwood had scooped up the ball and zig-zagged 71 yards for a score that should have restored a two-touchdown lead. The flag for illegal substitution wiped out the score, the Broncos went three-and-out.
Pittsburgh tied it at 27 on its next possession, with Wheaton scooting in from 9 yards out and dancing a little jig with Brown.